Drop on demand ink jet technology is widely used in the printing industry. Printers using drop on demand ink jet technology can use either thermal ink jet technology or piezoelectric technology. Even though they are more expensive to manufacture than thermal ink jets, piezoelectric ink jets are generally favored as they can use a wider variety of inks and reduce or eliminate problems with kogation.
Piezoelectric ink jet print heads typically include a flexible diaphragm and an array of piezoelectric elements (transducers) attached to the diaphragm. When a voltage is applied to a piezoelectric element, typically through electrical connection with an electrode electrically coupled to a voltage source, the piezoelectric element bends or deflects, causing the diaphragm to flex which expels a quantity of ink from a chamber through a nozzle. The flexing further draws ink into the chamber from a main ink reservoir through an opening to replace the expelled ink.
Increasing the printing resolution of an ink jet printer employing piezoelectric ink jet technology is a goal of design engineers. One way to increase the resolution is to increase the density of the piezoelectric elements.
As resolution and density of the print heads increase, the area available to provide electrical interconnects decreases. Routing of other functions within the head, such as ink feed structures, competes for this reduced space and places restrictions on the types of materials used. For example, current technology for use with a 600 dots-per-inch (DPI) print head can include parallel electrical traces on the flex circuit with each trace electrically connected to a pad (i.e., electrode) of the pad array (i.e., electrode array) of the flex circuit. The parallel traces can have a 38 micrometer (μm) pitch, a 16 μm trace width, leaving a 22 μm space between each trace. As print head densities increase, current flex circuit design practices will require formation of traces and pads having tighter tolerances and smaller feature sizes.